Electroabsorption modulator based on fermi level tuning

Abstract

A novel electroabsorption modulator based on tuning the Fermi level relative to mid-gap states in a semiconductor. The modulator includes a semiconductor waveguide that has an input port and an output port. Between the input port and the output port is a section of the waveguide that functions as an electroabsorptive region. Adjacent to the electroabsorptive region are electrical contacts. In operation by adjusting voltages on the electrical contacts, the quasi-Fermi level in the electroabsorptive region of the semiconductor waveguide is brought above or below mid band-gap electronic states. As these states transition between occupancy and vacancy, the absorption coefficient for optical radiation in the electroabsorptive region of the semiconductor changes. As this change in absorption coefficient modulates the intensity of transmitted radiation in response to an input data stream driving the voltages, the device functions as a semiconductor optical modulator in accordance with the principles of the invention.

1. A semiconductor electroabsorption modulator, comprising:
 a semiconductor wave guide having an input port configured to receive an input optical signal comprising a wavelength and an output port configured to transmit an output optical signal, said semiconductor wave guide having an electronic bandgap and an absorption coefficient for said wavelength, at least a portion of said semiconductor wave guide having at least one deliberately created electronic energy state within said electronic bandgap; and 
 at least one pair of electrodes disposed in proximity to at least a portion of said semiconductor wave guide, at least one electrode of said at least one pair of electrodes configured to receive an input data signal, 
 wherein in response to an application of said input data signal to said at least one electrode of said at least one pair of electrodes, said semiconductor electroabsorption modulator is configured to provide an output optical signal comprising a modulation component based upon a change in said absorption coefficient of at least a portion of said semiconductor wave guide, said modulation component configured to distinguish a one from a zero in a digital data stream; 
 wherein said change in said absorption coefficient of at least a portion of said semiconductor wave guide is responsive to a change in a Fermi level of said semiconductor wave guide, whereby a probability of occupancy of said at least one deliberately created electronic energy state within said electronic bandgap is modified. 
 
     
     
       2. The semiconductor electroabsorption modulator of  claim 1 , wherein said at least one deliberately created electronic energy state within said electronic bandgap is due to surface states of said semiconducting wave guide. 
     
     
       3. The semiconductor electroabsorption modulator of  claim 1 , wherein said at least one deliberately created electronic energy state within said electronic bandgap is due to ion implantation in said semiconductor wave guide. 
     
     
       4. The semiconductor electroabsorption modulator of  claim 1 , wherein said semiconductor wave guide is implemented in damaged silicon. 
     
     
       5. The semiconductor electroabsorption modulator of  claim 1 , wherein said semiconductor wave guide is implemented in a silicon-on-insulator configuration. 
     
     
       6. The semiconductor electroabsorption modulator of  claim 1 , wherein said semiconductor wave guide is implemented in a III-V compound semiconductor. 
     
     
       7. The semiconductor electroabsorption modulator of  claim 1 , wherein said semiconductor wave guide is implemented in an amorphous semiconductor. 
     
     
       8. The semiconductor electroabsorption modulator of  claim 1 , wherein said at least one electrode includes at least a top electrode disposed above said semiconductor wave guide, said top electrode separated from said semiconductor wave guide by an insulating layer. 
     
     
       9. The semiconductor electroabsorption modulator of  claim 1 , wherein said wavelength is a wavelength used in telecommunication. 
     
     
       10. The semiconductor electroabsorption modulator of  claim 9 , wherein said wavelength used in telecommunication is a wavelength in a selected one of a 1310 nm band, a 1490 nm band, and a 1550 nm band. 
     
     
       11. The semiconductor electroabsorption modulator of  claim 1 , wherein said wavelength is a wavelength in the range of 1 μm to 30 μm. 
     
     
       12. A semiconductor electroabsorption modulator, comprising:
 a semiconductor wave guide having an input port configured to receive an input optical signal comprising a wavelength and an output port configured to transmit an output optical signal, said semiconductor wave guide having an electronic bandgap separating a valence band and a conduction band and having an absorption coefficient for said wavelength, at least a portion of said semiconductor wave guide having deliberately created electronic energy states within said electronic bandgap, said deliberately created electronic energy states being separated from said valence band and from said conduction band; 
 at least one electrode disposed in proximity to at least a portion of said semiconductor wave guide, said at least one electrode configured to receive an input data signal, 
 wherein changing a voltage on said at least one electrode in response to said input data signal changes a probability of occupancy of said deliberately created electronic energy states within said electronic bandgap resulting in a change in said absorption coefficient for at least a portion of said semiconductor wave guide and a modulation of said output optical signal in response to said input data signal, said modulation configured to distinguish a one from a zero in a stream of digital data; 
 wherein said change in said absorption coefficient of at least a portion of said semiconductor wave guide is responsive to a change in a Fermi level of said semiconductor wave guide, whereby a probability of occupancy of said at least one deliberately created electronic energy state within said electronic bandgap is modified. 
 
     
     
       13. The semiconductor electroabsorption modulator of  claim 12 , wherein said deliberately created electronic energy states within said electronic bandgap are due to surface states of said semiconducting wave guide. 
     
     
       14. The semiconductor electroabsorption modulator of  claim 12 , wherein said deliberately created electronic energy states within said electronic bandgap are due to ion implantation in said semiconductor wave guide. 
     
     
       15. The semiconductor electroabsorption modulator of  claim 12 , wherein said semiconductor wave guide is implemented in damaged silicon. 
     
     
       16. The semiconductor electroabsorption modulator of  claim 12 , wherein said semiconductor wave guide is implemented in a silicon-on-insulator configuration. 
     
     
       17. The semiconductor electroabsorption modulator of  claim 12 , wherein said semiconductor wave guide is implemented in a III-V compound semiconductor. 
     
     
       18. The semiconductor electroabsorption modulator of  claim 12 , wherein said semiconductor wave guide is implemented in an amorphous semiconductor. 
     
     
       19. The semiconductor electroabsorption modulator of  claim 12 , wherein said at least one electrode includes at least a top electrode disposed above said semiconductor wave guide, said top electrode separated from said semiconductor wave guide by an insulating layer. 
     
     
       20. The semiconductor electroabsorption modulator of  claim 12 , wherein said wavelength is a wavelength used in telecommunication. 
     
     
       21. The semiconductor electroabsorption modulator of  claim 20 , wherein said wavelength used in telecommunication is a wavelength in a selected one of a 1310 nm band, a 1490 nm band, and a 1550 nm band. 
     
     
       22. The semiconductor electroabsorption modulator of  claim 12 , wherein said wavelength is a wavelength in the range of 1 μm to 30 μm. 
     
     
       23. A method of operating a semiconducting electroabsorption modulator, comprising the steps of:
 providing an input optical signal to an input port of a semiconductor wave guide, said semiconductor wave guide having at least one deliberately created electronic energy state in an electronic bandgap, and having an optical output port configured to provide an output optical signal; 
 changing a voltage on an electrode disposed in proximity to said semiconductor wave guide in response to an input data signal, said changing a voltage changing an absorption coefficient of said semiconductor wave guide, and said absorption coefficient is responsive to a change in a Fermi level of said semiconductor wave guide, whereby a probability of occupancy of said at least one deliberately created electronic energy state in said electronic bandgap is modified; and 
 transmitting said output optical signal from said optical output port, said output optical signal modulated in response to said input data signal.